The object of the present invention is a by-pass and pressure regulator valve. In particular, the valve is usefully applied internally of hydraulic circuits for high-pressure washing.
High-pressure washing plants generally comprise a piston pump, destined to place a washing fluid under pressure, a valve of the type of the invention and a lever tap valve, commonly called a gun, which is predisposed to enable an operator to control dispensing of the fluid.
Unless electrical devices are included for automatic turning-off of the pump, the pump operates continuously and thus remains in operation even when the gun is turned off by the operator; given the incompressibility of the fluid, it is necessary for it to be discharged into a low-pressure tank through a by-pass conduit. The opening of the conduit it controlled by a valve, simply known as a by-pass or unloader valve.
The valve is also used for control of the operating pressure with the gun open: this is normally done by partializing the opening of the by-pass hole. With the by-pass totally closed, the maximum operating pressure obtainable with the nozzle mounted on the gun is reached; by partially opening the by-pass a lower pressure is obtained. In substance, on exceeding a threshold pressure which can be adjusted, the hydraulic circuit starts to open on the by-pass conduit. In the example, adjustment mechanisms of known type are generally used, being constituted by an obturator maintained in a seating by a pre-loaded spring.
Less sophisticated by-pass valves are commanded by the pressure peak created in the fluid on closing the gun: the fluid is trapped by a check needle which isolates the delivery branch and is used to pilot the opening of the by-pass hole. Devices of this type, however constructionally very simple and reliable they are, exhibit an obvious drawback; the delivery channel upstream of the gun stays at high pressure, with obvious problems in terms of safety and ease of use. With the gun closed, the washing fluid will be maintained at a sufficiently high pressure to keep the by-pass valve open, with pressure levels therefore above the normal working pressure.
Improved by-pass valves, commonly known as reset valves, can be used to solve the above-described problem. They are controlled not by the pressure peak internally of the channel, but by the washing fluid flow directed to the dispensing gun. Valves of this type usually include a device destined to cause a flow pressure loss in the fluid crossing it and a pilot plate governed by the pressure differences generated, which determines the closure of the by-pass branch in response to the flow pressure loss. The flow pressure loss is obviously annulled with the closure of the gun and the consequent interruption of the fluid flow.
Differently to what happens in a normal unloader valve, in a reset valve the delivery conduit is connected to the by-pass even with the gun closed thanks to the absence of the check needle: the pressure peak generated by the interruption of the flow does not thus remain trapped but can be discharged through the by-pass hole which opens in response to the lack of flow. With the gun closed the delivery branch is thus at a pressure which is hardly above atmospheric pressure.
Valves of the described type generally integrate, in a single device, the described pressure reset functions in the delivery branch and an operating pressure control function. A common solution consists in associating an end of the pressure control spring to the pilot plate, and the other end of the spring to the stem which commands the obturator of the valve. In this way, the spring is compressed by the plate only in the presence of a flow pressure loss through the flow conduit; in this configuration it tends to keep the obturator in a position of closure of the by-pass branch and exerts its action of control over the operating pressure. With the spring unloaded, i.e. in the absence of a flow pressure loss, no action is exerted on the obturator to keep it in its seating, so it opens on the by-pass branch at low pressure.
The above-described valve exhibits, however, a substantial problem: to keep the obturator closed the regulator spring has to be contrasted. Since this is usually a rather strong spring, the flow pressure loss generated by the device has to be quite strong. There is a consequent considerable reduction in the dispensing pressure of the washing fluid, which causes a high consumption of energy and leads to problems of overheating in the plant's pump.
Further, as it is always necessary to have large flow pressure loss in order to guarantee the obturator seal on the by-pass seating, plant functioning problems may ensue at low flow rates.
In order to operate with limited flow pressure loss, it is thus necessary to separate the pilot piston from the contrast spring, such that it is only subject to the forces deriving from the pressure differential to which it is subjected. In this case, however, the mechanism is particularly sensitive and has therefore to be calibrated with extreme precision. With respect to this necessity, known-type valves are limited by the variations in the flow pressure loss due to fluctuations in the fluid flow rate and functioning irregularities due to contact of one of the pilot piston surfaces with the fluid in motion.
In some reset valves made according to the prior art, the separating of the contrast spring of the pilot piston for closure of the by-pass is realised by providing two different by-pass holes, possibly connected to one another, closure of which is commanded by two distinct obturators, one of which is governed by the operating pressure regulation device, the other of which is controlled by the mechanism for resetting the pressure on closure of the gun. The presence of two distinct mechanisms leads however to an undesired increase in size and an excessive constructional complexity.
The aim of the by-pass and pressure regulator valve of the present invention is to resolve the above-described drawbacks in the prior art.
The main advantage of the by-pass and pressure regulator valve of the present invention lies in the limited flow pressure loss induced by the passage of the dispensed fluid through the device; this flow pressure loss is comparable in extent to that of a normal unloader valve.
A further advantage of the valve of the invention is its compactness, with positive consequences such as a smaller overall size, a limited number of components and a simplification of the production process therefore.
A further substantial advantage of the device of the present invention relates to the broad range of flows for which it can be used, without any deterioration of the operating performance thereof.
A still further advantage of the invention derives from the easy and accurate calibration of the device which leads to high levels of reliability thereof.
A further advantage of the valve derives from the possibility of associating a micro-switch thereto which is destined to electrically control the turning-off of the pump or other electrical or electromechanical devices of the hydraulic circuit in response to the closure of the dispensing gun.